The purpose of the study is to determine which of three combinations of antiretroviral therapy provides the greatest reduction in viral load in a cohort of HIV infected children who are clinically stable. Safety and tolerance based on both clinical and laboratory toxicities will also be monitored. At the end of the study it is expected that we will be able to recommend one of these combinations as most appropriate for Phase III studies. The three combination therapies are the following: ZDV plus 3TC vs. D4T plus Ritonavir vs. ZDV plus 3TC plus Ritonavir. (ACTG 388 V. 2)